Don't know port from starboard? The Misunderstood Mariner helps make the world of ships and the people who run them understandable and interesting. Along the way, we'll talk about how important the maritime industry is to the modern world, especially economically. Welcome aboard!

Wednesday, September 14, 2011

Dynamic Positioning

One of the truisms of the oil industry in general and the offshore drilling industry in particular is that all the easy-to-get-to oil was extracted first. Shallow-water oil fields were drilled first so, as time went on, oil rigs moved into deeper and deeper water. Eventually, oil was being drilled for in areas where the water is too deep to build a rig on the bottom itself, or even to practically anchor a rig or drillship. Thus, it became necessary to find a way to keep an oil rig or drillship in a single position while floating on the surface. This led to the development of dynamic positioning.

Dynamic positioning (DP) is a system that keeps a vessel in a single position at a constant heading using only its own propellers and thrusters. The first DP vessel was the CUSS 1 (pictured above). CUSS 1 was not an oil industry vessel, but a scientific expedition to drill for core samples of the Earth's crust. In 1961, CUSS 1 held position in 11,700 feet off Mexico and drilled up to 600 feet into the sea bed. CUSS 1 held position using radar and sonar, a human operator, and four steerable propellers that were installed on the ship. Modern DP vessels use advanced computer systems, position-finding systems ranging from GPS to weights on a wire, heading-finding methods using a gyrocompass or more advanced system, and a variety of thrusters, all depending on the vessel and its mission.

DP allows a level of position-keeping not previously available, making it very useful outside of drilling operations as well. For instance, with DP two vessels can maintain position near each for cargo or crew transfers without tying off to each other. Other tasks like cable-laying or salvage may also be simplified by DP. Even the private yacht industry has adopted DP, whether for close-quarters ship handling in crowded marinas or maintaining the cocktail hour crowd's view of a particularly spectacular sunset.

DP is largely computer controlled, but human operators are required to monitor the system and to take over when things go wrong. Because DP-equipped ships are often conducting precise operations, the consequences of a failure can be fatal. Thus, DP operators go through a long and expensive training and certification program consisting of several weeks of classroom time combined with months of at-sea experience. On the other hand, DP operators also command top wages in the maritime industry, often earning $900 or more per day.